1. Field of the Invention
This invention relates to synthetic resin granulating dies, and more particularly to a synthetic resin granulating die having heat insulating structure which is applicable to an underwater granulating machine.
2. Related Art
In an underwater granulating machine, the surface of its granulating die is cooled with circulating water, and therefore sometimes molten resin is solidified in the nozzles of the granulating die; in other words, they are so-called "clogged up". In order to prevent the "clogged up" phenomenon, the present Applicant has before proposed a synthetic resin granulating die which has the following structure and function.
FIG. 3 shows the left half of the granulating die. FIG. 4 is an enlarged diagram of the part B of FIG. 3. More specifically, the part (a) of FIG. 4 is a diagram showing the arrangement of a nozzle section, and the part (b) of FIG. 4 is a sectional view taken along line C--C in the part (a) of FIG. 4.
As shown in FIGS. 3 and 4, the granulating die 1 has an outside annular path 5, and an inside annular path 6. And a number of heating jackets 3 are provided between the two annular paths 5 and 6. The outside annular path 5 is divided into upper and lower outside annular paths 5a and 5b by right and left blocks 7. The upper and lower outside annular paths 5a and 5b have a heating-fluid lead-in path 8 and a heating-fluid lead-out path 9, respectively. A vacuum heat-insulating layer 4, which is sealed by electronic beam welding, is formed on the surface side of the granulating die in such a manner that it is adjacent to each of the heating jackets 3. A number of nozzles holes 2 are formed between the heating jackets 3. A hardening layer 13 is provided in the surface of the granulating die between the outside annular path 5 and the inside annular path 6. A flange 10 is mounted on the periphery of the granulating die 1. Circulating-box mounting bolt holes 11, and granulating-die mounting bolt holes are formed in the flange 10 thus mounted.
Now, the function of the above-described granulating die will be described.
The heating fluid introduced through the lead-in path 8 is passed through one outside annular path 5a, the heating jackets on both sides of the lines of the nozzles holes, and the inside annular path 6 (a part of the heated fluid passing through only the heating jackets), and then discharged through the other outside annular path 5b. The surface of the granulating die 1 is cooled being in contact with the circulating water. On the other hand, the vacuum heat-insulating layers 4 are formed on the surface side of the granulating die 1 in such a manner that they are adjacent to the heating jackets 3, and therefore the cooling is interrupted, and the nozzle holes 2 are sufficiently heated by the heating fluid flowing through the heating jacket, which prevents the solidification of molten resin at the nozzle holes 2.
In the above-described conventional granulating die, the vacuum heat-insulating layers are formed on the surface side thereof, which improves the heat-insulating effect. However, the heating-insulating effect is only for the region where the hardening layer is provided which is between the outside annular path and the inside annular path. Hence, the surfaces of the die which are inside and outside of the hardening layer is cooled with the circulating water in the circulating box, so that the temperature of the whole die is decreased. On the other hand, a granulating die is known in the art in which a resin gasket is mounted on the surface of the die except the hardening layers, and is retained with a retaining board of stainless steel, thereby to prevent the decrease in temperature of the whole die. However, the granulating die suffers from the following difficulties. That is, the higher the resin gasket is in heat insulating, the more it is liable to be deteriorated by heat. Therefore, it is soon broken, and accordingly it is necessary to replace it frequently.